1. Field of the Invention
This invention relates to an optical disk drive apparatus. More particularly, this invention relates to a method for seeking spiral tracks of an optical disk.
2. Description of the Related Art
FIG. 6 shows how spiral tracks are formed on an optical disk. In the figure, t1, t2, t3,, etc. are track identification numbers and s1, s2, s3, etc. are sector identification numbers, respectively. Each sector contains a track identification number and a sector identification number. In spiral tracks, track identification numbers change as one crosses the track boundary 120.
If a seek operation is performed from the current position of a track identification tA to the target position of a track identification tB, a number equal to a track distance Delta t(=tB-tA) is held in a track number counter. The track crossing signals generated during a seek operation are counted and the seek operation is continued until the number of track crossing signals counted is equal to the value (Delta t) held in the track number counter. However, it is difficult to properly reach a target position by the mere counting of track crossing signals equal to a track distance (Delta t) when a seek operation for spiral tracks is performed. It is, therefore, difficult to reach the target position in a short time.
It is clear that for spiral tracks, if an optical head does not move at all in the radial direction of the disk (not perform a seek operation), a track crossing signal is generated in response to the optical head crossing the track boundary once each time the disk rotates once. On the other hand, if the disk does not rotate at all, the number of tracks through which the optical head passes during a seek operation (that is, the number of track crossing signals) accords with a track distance (Delta t). Thus, with spiral tracks, the number of times the optical head crosses a track during a seek operation within the range of a track distance (Delta t) does not necessarily accord with the track distance (Delta t) because of the rotation of the disk during seek operation.
To avoid this problem with respect to reaching a target track, Japanese Published Unexamined Patent Application (PUPA) No. 1-130327 discloses a method of reaching the target track wherein a detector is provided to actually detect the rotation number of the disk during a seek operation. A seek operation is continued until the track crossing signals counted are equal to a track distance (Delta t) and then an additional seek operation occurs wherein track crossing signals counted are equal to the number of rotations of the disk detected by said detector.
This method is weak in that two seek operations are needed to finally reach a target position. Thus, it is impossible to reach the target position in a short time.